Coating composition for thermoplastic resin particles for forming foam containers

ABSTRACT

Expandable or pre-expanded thermoplastic particles, e.g. polystyrene particles, used to form foam containers e.g. cups, bowls, are coated with a coating composition comprising a liquid part consisting of a) liquid polyethylene glycol with an average molecular weight of 200 to 800; and a solid part comprising components selected from the group consisting of b) polyolefin wax, e.g. polyethylene wax, c) a metal salt of higher fatty acids, e.g. zinc stearate or calcium stearate; d) polyethylene glycol with an average molecular weight of 900 to 10,000; and e) a fatty bisamide or fatty amide, e.g. ethylene bis-stearamide; and combinations of b) through e). The coating composition prevents or resists leakage of liquids and foods with oil and/or fatty components and improves the rim strength and ATF properties of foam containers.

This is continuation of application U.S. Ser. No. 12/769,716 filed Apr.29, 2010, now U.S. Pat. No. 7,785,711, which is a divisional applicationof application U.S. Ser. No. 11/480,591 filed Jul. 3, 2006, now U.S.Pat. No. 7,736,740; which is a division of application U.S. Ser. No.10/769,349 filed on Jan. 31, 2004, now U.S. Pat. No. 7,294,655, whichapplication claims the benefit of U.S. Provisional Application No.60/444,897 filed Feb. 4, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to thermoplastic resin particles forforming foam containers, such as cups, bowls, etc.; to a molded article,e.g. foam container made from the resin particles; to a coatingcomposition for the thermoplastic resin particles; and to a method forimproving the resistance to leakage of a foam container. Moreparticularly, the present invention pertains to a coating compositionfor expandable or pre-expanded, i.e. “pre-puff”, thermoplastic resinparticles, e.g. polystyrene, used in molding containers for carryingliquids, e.g. coffee or foods containing oil and/or fat components suchas precooked (instant noodles, soups, sauces, fried chicken)fat-containing foods, and the like.

2. Background Art

The manufacture of molded articles, e.g. containers, e.g. cups, bowls,made from expandable thermoplastic particles is well known. The mostcommonly used thermoplastic particles are expandable polystyreneparticles, referred to as “EPS” particles. Typically, polystyrene beadsare impregnated with a blowing agent, which boils below the softeningpoint of the polystyrene and causes the impregnated beads to expand whenthey are heated. When the pre-expanded beads are heated in a moldcavity, they further expand to fill the cavity and fuse together to forma shaped article, e.g. containers, e.g. cups, bowls, etc.

The formation of molded articles from impregnated polystyrene beads isgenerally done in two steps. First, the impregnated polystyrene beadsare pre-expanded to a density of from about 2 to 12 pounds per cubicfoot. The pre-expanded beads are typically called “pre-puff”. This firststep, i.e. the pre-expansion step, is conventionally carried out byheating the impregnated beads using any conventional heating medium suchas steam, hot air, hot water, or radiant heat. Second, the pre-expandedbeads (“pre-puff”) are heated in a closed mold to further expand thepre-expanded beads to form a fused article having the shape of the mold.This latter step is generally referred to as molding.

The expandable polystyrene particles used to make foam containers aregenerally prepared by an aqueous suspension polymerization process,which results in beads that can be screened to relatively precise beadsizes. Typically, bead diameters are within the range of from about0.008 to about 0.02 inch. Occasionally, cups are made from particleshaving bead diameters as much as 0.03 inches.

In spite of careful bead size control, one problem, which continues toplague the container, industry is that after a period of time the EPScontainers have a tendency to leak coffee or to leak the oil and/or fatcomponents in food substances carried by the containers. That is, thecoffee or the oil and/or fat permeate around the fused polystyrene beadsand through the wall of the container. With regard to the oil and/or fatcomponents, a stain generally forms on the outer surface of thecontainer.

Several approaches have evolved over the years directed toward thereduction of leakage in containers for retaining liquids and/orpre-cooked foods.

Amberg et al., U.S. Pat. No. 4,036,675 discloses a container made fromfoamed polystyrene, which is lined on one or both sides with unorientedpolyolefin film, preferably polypropylene. The film is secured to thefoamed plastic base material using a vinylic polymer or polyamide resinas a heat-sensitive adhesive. The film is coated with a wet adhesive anddried before laminating the film to the foam material.

Sonnenberg U.S. Pat. Nos. 4,703,065 and 4,720,429 disclose thermoplasticpolymer foam cups for retaining coffee that are molded fromthermoplastic polymer particles whose surfaces are coated with afluorosurfactant before molding.

Sonnenberg U.S. Pat. No. 4,785,022 discloses a method for enhancing thecoffee retention of molded foam cups. The method involves coating theexpandable polystyrene particles with various rubber polymers andcopolymers, e.g. polybutene, polyisobutylene, isobutylene-butenecopolymer and butene-ethylene copolymer.

Arch, et al. U.S. Pat. No. 4,798,749 and U.S. Pat. No. 4,840,759overcome the problem of coffee leakage by replacing conventional blowingagents such as butanes, n-pentane, hexanes, and the halogenatedhydrocarbons with isopentane in the expandable styrene polymerparticles.

Ikeda, et al., U.S. Pat. No. 4,698,367 discloses expandablethermoplastic resin particles composed of a fluorinated vinyl polymerand a hydrophilic vinyl polymer that covers or is included on thesurface or in the surface layer of the expandable thermoplasticparticle. These resin particles are useful for producing packagecontainers for oily or fatty foods.

Sakoda et al., U.S. Pat. No. 6,277,491 B1 discloses coating the surfaceof the resin beads or incorporating resin beads with afluorine-containing block copolymer comprising a fluorine-containingvinyl-type polymer segment derived from a fluorine-containing vinyl-typemonomer and a lipophilic vinyl-type polymer segment derived from alipophilic vinyl-type monomer.

Suzuki et al., U.S. Pat. No. 4,206,249 discloses a process for producinga paper container having high impermeability to liquid which comprisesspray coating a polymerizable solution containing a pre-polymer onto awall surface of a paper container and irradiating the coated wall withultraviolet light to effect the setting of the pre-polymer on the wallsurface of the container. This forms a coating, which is impermeable toliquids, such as water, milk, soft drinks, oils, etc.

Breining, et al., U.S. Pat. No. 6,416,829 B2 discloses a heat insulatingpaper cup where the body member is coated on its outside surface with afoamed low density polyethylene, and on its inside surface with anunfoamed modified low density polyethylene.

Japan Unexamined Patent Publication JP2002338725A (Kaneka Corporation)discloses the use of a volatile foaming agent containing 30 to 60% byweight based on the foaming agent of isopentane. The expandablepolystyrene resin particles are covered with zinc stearate rangingbetween 0.2 to 0.5 parts by weight based on 100 parts by weight of resinparticle. The amount of foaming agent ranges from 0 to 5.5% by weight ofthe resin particles.

None of the thermoplastic resin particles of the prior art for makingfoam containers are coated or covered with a liquid polyethylene glycoland then with one or more components selected from the group consistingof polyolefin wax, e.g. polyethylene wax; a metal salt of higher fattyacids, e.g. zinc stearate; polyethylene glycol; and a fatty bisamide orfatty amide, e.g. ethylene bis-stearamide, for reducing or eliminatingthe penetration of liquid and/or oil and/or fat components of food itemssuch as coffee, noodles, soups, sauces, stews, meats, and the likethrough the foam containers.

SUMMARY OF THE INVENTION

The invention meets the above need. The invention particularly relatesto expandable thermoplastic particles, preferably polystyrene particles,for making molded articles, e.g. foam containers, e.g. bowls, cups,etc., which containers adequately retain oils and flavorings in fooditems such as instant noodles, etc., and liquids such as hot coffee orhot water added to food items such as instant soups or noodles, stews,meats or the like.

Expandable or pre-expanded (sometimes referred to as “pre-puff”)thermoplastic particles are coated or covered with a coatingcomposition. The resultant containers are less pervious to leakageand/or stains caused by liquids and/or oily and fatty foods.

The coating composition essentially comprises two parts, 1) a liquidpart and 2) a powder or solid part. The liquid part comprises a) greaterthan about 0.01% by weight, based on the weight of the particles, ofpolyethylene glycol having an average molecular weight ranging fromabout 200 to about 800 (PEG 200-PEG 800), and the solid part comprisescomponents selected from the group consisting of: b) greater than about0.01% by weight, based on the weight of the particles, of polyolefinwax; c) greater than about 0.01%, based on the weight of the particles,of a metal salt of higher fatty acids; d) greater than about 0.01%,based on the weight of the particles, of polyethylene glycol having anaverage molecular weight ranging from 900 to about 10,000 (PEG 900-PEG10,000), and e) greater than about 0.01%, based on the weight of theparticles, of a fatty bisamide or fatty amide, e.g. ethylenebis-stearamide, and combinations of b) through e).

For expandable particles, it is preferable to use component a) and oneor more of components b) through e). For pre-expanded or “pre-puff”particles, component a) is optional, and one or more of components b)through e) are used.

A preferred embodiment is a coating composition comprising a) about0.30% by weight of polyethylene glycol having an average molecularweight of 400 (PEG 400 in liquid form); b) about 0.40% by weight ofpolyolefin wax, preferably polyethylene wax, and c) about 0.105% byweight of a metal salt of higher fatty acid, preferably zinc stearate.

Preferably, expandable thermoplastic particles are first coated with theliquid polyethylene glycol and then coated with the solid components ofthe coating composition of the invention. The solid componentspreferably are mixed or blended together and then mixed or blended withthe thermoplastic particles. For pre-expanded particles, as statedhereinabove, the use of the liquid polyethylene glycol is optional. Thesolid components preferably are mixed or blended together and then mixedor blended with the thermoplastic particles.

The invention also relates to a method for improving the resistance toleakage of molded articles, e.g. foam containers, e.g. cups, bowls, etc.made from thermoplastic resin particles. The method involves, preferablyfor expandable particles, first applying component a) to the particlesand then applying one or more of the solid components of the coatingcomposition to the expandable particles. For pre-expanded particles, themethod involves, optionally applying component a) to the particles, andapplying one or more of the solid components of the coating compositionto the pre-expanded particles.

It is therefore an object of the present invention to provide moldedarticles, e.g. foam containers which exhibit improved resistance toleakage and therefore improved resistance to stain at least on the outersurface of the containers, and which exhibit improved mechanicalproperties, such as improved rim strength.

It is a further object of the present invention to provide a coatingcomposition for thermoplastic particles used to form foam containersthat are suitable for retaining oily or fatty food items, such asnoodles, soups, sauces, stews, meats, and the like, or for retainingliquids such as hot coffee or hot water for instant noodles, soups,stews, etc., and which foam container has at least improved ATFproperties and/or improved rim strength properties.

A still further object of the present invention is to provide expandableor pre-expanded thermoplastic particles comprising a coatingcomposition, which increases the integrity of foam articles made fromthe particles.

And yet a still further object of the present invention is to provide amethod for improving the resistance to leakage of a foam container byproviding a coating composition for coating thermoplastic resinparticles used to form the foam container.

These and other object of the present invention will be betterappreciated and understood by those skilled in the art from thefollowing description and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “coat” means to contact with a coatingcomposition so as to place a substantial portion of the components ofthe coating composition of the invention on or near the surface orsurfaces of the resin particles being contacted.

As used herein, the term “cover” means principally in the form in whichthe coating composition adheres in layers on the surface of the resinparticles.

The coating composition of the invention essentially comprises twoparts, 1) a liquid part and 2) a powder or solid part. The liquid partcomprises a) greater than about 0.01% by weight, based on the weight ofthe particles, of polyethylene glycol having an average molecular weightranging from about 200 to about 800 (PEG 200-PEG 800). Preferably, theweight percent of the liquid polyethylene glycol is 0.01% by weight toabout 0.80% by weight, based on the weight of the particles. The solidpart of the coating composition of the invention comprises componentsselected from the group consisting of: b) greater than about 0.01% and,preferably 0.01% to about 1.0% by weight, based on the weight of theparticles, of polyolefin wax, preferably polyethylene wax; c) greaterthan about 0.01%, and preferably 0.01% to about 0.60% by weight, basedon the weight of the particles, of a metal salt of higher fatty acid,preferably zinc stearate; d) greater than about 0.01%, and preferably0.01% to about 0.80% by weight, based on the weight of the particles, ofpolyethylene glycol having an average molecular weight ranging from 900to about 10,000 (PEG 900-PEG 10,000), and e) greater than about 0.01%,and preferably 0.01% to 1.0% by weight, based on the weight of theparticles, of a fatty amide or fatty bisamide, e.g. ethylenebis-stearamide, and combinations of components b) through e).

For expandable beads, i.e. dense beads, the coating compositionpreferably comprises component a) and at least one or more of componentsb) through e) in combination with component a). For example, thecombinations may be comprised of components a) and b); or components a)and c); or components a) and d); or components a) and e); or componentsa), b), and c); or components a), c), and d); or components a), b), andd); or components a), b), and e); or components a), c), and e); orcomponents a), d), and e); or components a), b), c), and d); orcomponents a), b), c), and e); or components a), c), d), and e); orcomponents a), b), d), and e); or components a), b), c), d), and e).

For pre-expanded particles or “pre-puff” particles, the liquid part isnot necessary but in some instances may be preferred, for reasonsdiscussed herein below. For the pre-expanded particles, the solid partof the coating composition will comprise at least of one or more ofcomponents b) through e), which may be in combinations similar to thoselisted in the preceding paragraph for expandable particles.

Any of components a) through e) must be present in an amount greaterthan or equal to 0.01% by weight, if used alone. If component b) is usedit should be present in an amount that is at least 0.01% to about 1.0%by weight, based on the weight of the particles. If component d) is usedit should be present in an amount that is at least 0.01% to about 0.8%by weight, based on the weight of the particles. If components b) and d)are used, then preferably both components b) and d) would be present togive a combined weight percent of about 0.01 to about 1.8% by weightbased on the weight of the particles. This is an example of a desirabletotal weight percentage for a combination of components b) and d).Desirable total weight percentages for other combinations of componentsb) through e) will be apparent to those skilled in the art.

The expandable, and therefore, the pre-expanded thermoplastic particlescan be made from any suitable thermoplastic homopolymer or copolymer.Particularly suitable for use are homopolymers derived from vinylaromatic monomers including styrene, isopropylstyrene,alpha-methylstyrene, nuclear methylstyrenes, chlorostyrene,tert-butylstyrene, and the like, as well as copolymers prepared by thecopolymerization of at least one vinyl aromatic monomer with monomerssuch as divinylbenzene, butadiene, alkyl methacrylates, alkyl acrylates,acrylonitrile, and maleic anhydride, wherein the vinyl aromatic monomeris present in at least 50% by weight of the copolymer. Styrenic polymersare preferred, particularly polystyrene. However, other suitablepolymers may be used, such as polyolefin, e.g. polyethylene,polypropylene, and mixtures thereof.

In the embodiments herein, the expandable thermoplastic particles areexpandable polystyrene (EPS) particles. These particles can be in theform of beads, granules, or other particles convenient for the expansionand molding operations. Particles polymerized in an aqueous suspensionprocess are essentially spherical and are preferred for molding orforming the foam container of the invention. These particles aretypically screened so that their size ranges from about 0.008 to about0.02 inch, and in some instances ranges from about 0.008 to about 0.03inch.

The thermoplastic particles are impregnated using any conventionalmethod with a suitable blowing agent. For example, the impregnation canbe achieved by adding the blowing agent to the aqueous suspension duringthe polymerization of the polymer, or alternatively by re-suspending thepolymer particles in an aqueous medium and then incorporating theblowing agent as taught in U.S. Pat. No. 2,983,692 to D. Alelio. Anygaseous material or material which will produce gases on heating can beused as the blowing agent.

In the present invention, the blowing agent can be aliphatichydrocarbons, such as acetone, methyl acetate, butane, n-pentane,cyclopentane, isopentane, isobutene, neopentane, and mixtures thereof. Apreferred blowing agent is normal pentane and mixtures of pentanes i.e.normal pentane, isopentane and/or cyclopentane. Other blowing agentsthat can be used in the invention are halogenated hydrocarbons, e.g.HFC's, CFC's and HCFC'S, and mixtures thereof. For the expandableparticles of the invention, any of the preceding blowing agents may alsobe used in combination with carbon dioxide, air, nitrogen, and water.

The blowing agent level of the polymer particles generally will be lessthan 10.0 weight percent, preferably, less than 9.0 weight percent, andmost preferably will range from between about 3.0 weight percent toabout 6.0 weight percent based on the weight of the thermoplastic resincomposition.

Alternatively, water can be blended with the aliphatic hydrocarbonsblowing agents or water can be used as the sole blowing agent as taughtin U.S. Pat. Nos. 6,127,439; 6,160,027; and 6,242,540 assigned to NOVAChemicals (International) S.A. In these patents, water-retaining agentsare used. The weight percentage of water for use as the blowing agentcan range from 1 to 20%. U.S. Pat. Nos. 6,127,439, 6,160,027 and6,242,540 in their entirety are incorporated herein by reference.

The impregnated thermoplastic particles can be foamed cellular polymerparticles as taught in Arch et al. U.S. patent application Ser. No.10/021,716 assigned to NOVA Chemicals Inc. The foamed cellular particlesare preferably polystyrene that are pre-expanded to a density of fromabout 12.5 to about 34.3 pounds per cubic foot, and which contain avolatile blowing agent level that is less than 6.0 wt %, preferablyranging from about 2.0 wt % to about 5.0 wt %, and more preferablyranging from about 2.5 wt % to about 3.5 wt %, based on the weight ofthe polymer.

The impregnated expandable thermoplastic particles are generallypre-expanded to a density of from about 2 to about 12 pounds per cubicfood prior to molding. The pre-expansion step is carried outconventionally by heating the impregnated beads via any conventionalheating medium, e.g. steam, hot air, hot water, or radiant heat. Onegenerally accepted method for accomplishing the pre-expansion ofimpregnated thermoplastic particles is taught in U.S. Pat. No. 3,023,175to Rodman.

The pre-expanded beads are heated in a closed mold to further expand thepre-expanded particles to form a foam article, i.e. container.

In an embodiment of the invention, expandable, i.e. impregnatedthermoplastic particles are covered or coated with component a), theliquid polyethylene glycol, and then covered or coated with the solidcomponents of the coating composition of the invention prior to theparticles being subjected to pre-expansion and molding steps. Anyconventional method of coating or covering particles may be utilized inthe invention.

In a further embodiment of the invention, the expandable particles arepre-expanded and the pre-expanded thermoplastic particles are coated orcovered with the liquid polyethylene glycol and then coated or coveredwith the solid components of the coating composition of the inventionprior to the particles being subjected to the molding step.

It is to be understood that in some instances the pre-expanded particlesdo not need to be coated with the liquid polyethylene glycol in that thepre-expanded particles generally have a rougher surface finish and agreater surface area for the adherence of the solid components of thecoating composition compared to expandable particles that generally havea smooth surface finish and less surface area. However, it has beenfound by the inventors that the liquid polyethylene glycol tends tolessen the static electricity generally associated with pre-puffparticles, especially during the conveyance of these particles via airflow from one piece of plant equipment to another piece of plantequipment. Thus, the application of the liquid polyethylene glycol onpre-expanded or pre-puff particles may be desirable in some instances.

The liquid polyethylene glycol and the solid components of the coatingcomposition cover or coat or can be included on the surfaces of theexpandable thermoplastic resin particles. As stated herein above, theterm “cover” means principally in the form in which the coatingcomposition adheres in layers on the surface of the resin particles.This can be achieved by first contacting the resin particles with theliquid polyethylene glycol and then sufficiently mixing the resinparticles with the solid components of the coating composition in amixer, such as a drum blender, ribbon blender, V blender, Henschelmixer, Ledage mixer, a high intensity mixer, a low intensity blender,and the like.

The solid components of the coating composition preferably are in powderform. However, the powder form may be made into liquid form bydissolving the powder in solvent or dispersing the powder in water.

Preferably, the thermoplastic particles are contacted first with theliquid polyethylene glycol and then contacted with one or more of thesolid components of the coating composition of the invention, asdiscussed herein above. The solid components preferably are mixed orblended together and then blended or mixed with the thermoplasticparticles.

The polyolefin wax of component b) is selected from the group consistingof polyethylene wax and polypropylene wax, and preferably ispolyethylene wax. The polyolefin wax has an average molecular weight ofabout 650 to about 30,000; preferably is in powder form; and has aparticle size ranging from about 1 to about 140 microns in diameter,preferably, about 6 microns.

The metal salt of higher fatty acids used as component c) in the coatingcomposition is selected from the group consisting of zinc, magnesium,calcium or aluminum salts of stearic, lauric or myristic acid, of whichzinc stearate is preferable.

For a preferred embodiment the coating composition of the inventioncomprises: component a), polyethylene glycol, in an amount of about0.30% by weight, based on the weight of the particles, and having anaverage molecular weight of about 400 (PEG 400 in liquid form);component b), polyolefin wax, preferably polyethylene wax, in an amountof about 0.40% by weight, based on the weight of the particles, andhaving a particle size of about 6 microns and an average molecularweight of 1,000; and component c), a metal salt of higher fatty acids,preferably zinc stearate, in an amount of about 0.105% by weight, basedon the weight of the particles.

In applying the coating composition to the particles, as stated hereinabove, it is preferable to first cover the resin particles with liquidpolyethylene glycol, which is believed to modify the surface tension,i.e. make the surface more hydrophilic, and which is an adhering agentfor the coating composition, and then to cover the resin particles withthe solid components of the coating composition.

Preferably, the liquid polyethylene glycol has an average molecularweight of about 200 to about 800 (PEG 200-PEG 800), and preferably, hasan average molecular weight ranging from about 300 to about 600. Ingeneral, the number appearing after the designation “PEG” (polyethyleneglycol) indicates the average molecular weight, e.g. PEG 200 representspolyethylene glycol with an average molecular weight of about 200, etc.

The amount of liquid polyethylene glycol is greater than 0.01 andpreferably is 0.01% to about 0.80% by weight, based on the weight of theparticles, and preferably ranges from about 0.05 to about 0.50% byweight, based on the weight of the particles.

The coating composition covers the thermoplastic resin particlespreferably in an amount of 0.005 to 2.0% by weight based on the weightof the particles, and more preferably 0.01 to 1.0% by weight, based onthe weight of the thermoplastic resin particles. If the coverage of thecoating composition is less than 0.005% by weight, the effect of theprevention of leakage of the liquid or fatty/oil components of thecontainer is generally insufficient, and if the coverage exceeds 2.0% byweight, there may be a tendency to increase the amount of lumping in thepre-expansion of the particles or there may be a tendency to retard thefusing together of the thermoplastic particles in the molding process.

A method of the invention relates to the expandable and optionallypre-expanded thermoplastic particles first being coated with thecomponent a), i.e. the liquid polyethylene glycol e.g. PEG 400,component, and then blending the particles with a mixture of the solidcoating composition. If the coating composition is applied to expandablethermoplastic particles, these particles are then pre-expanded, and fedto the mold. If the coating composition is applied to pre-expandedthermoplastic particles, these particles are then fed to the mold.

Polyethylene glycols suitable for use in the coating composition of theinvention are represented by the following general formula:H(OCH₂CH₂)_(n)OH

Polyethylene glycols having the above general formula are commerciallyavailable from BASF under the trademark PLURACOL®.

Polyethylene waxes suitable for use in the coating composition of theinvention are represented by the following general formula:(—CH₂CH₂—)_(n)

Polyethylene waxes having the above general formula are commerciallyavailable from Baker Petrolite under the trademark PETROLITE®.Preferably, polyethylene waxes having an average molecular weightranging from about 650 to about 30,000 and a particle size rangingbetween 1 micron and 140 microns are used in the coating composition ofthe invention.

Zinc stearates suitable for use in the coating composition of theinvention are represented by the following general formula:[CH₃(CH₂)₁₆CO₂]₂Zn

Zinc stearates having the above general formula are commerciallyavailable from Ferro under the trademark SYNPRO®.

Ethylene bis-stearamides suitable for use in the coating composition ofthe invention are represented by the following general formula:CH₃(CH₂)₁₆CONH—(CH₂)₂NH—(CH₂)₁₆CH₃

Ethylene bis-stearamide having the above general formula arecommercially available from the Crompton Corporation under the trademarkKEMAMIDE® W-40.

In addition to substantially coating or covering the thermoplastic resinparticles with the coating composition of the invention, an alternateapproach is to add the coating composition at the time of impregnatingthe thermoplastic resin particles with a blowing agent to retain thecoating composition in the surface layer of the resin beads.

Preferably, the entire surface of the thermoplastic resin particles isto be coated or covered with a thin film or layer of the coatingcomposition. However, it may be adequate for the purposes of theinvention if only a portion of the surfaces of the particles is coatedor covered with the coating composition of the invention.

The foam container may be a polystyrene cup that may be fabricated by aconventional cup-forming machine that has an inner shell and an outershell. An example of this type of machine is MODEL 6-VLC-125 machinemade by Autonational B.V. Impregnated thermoplastic particles are eitheraged or un-aged, are coated with the coating composition, arepre-expanded, and are then fed to a conventional cup-forming machine.

The cup fabrication rate for a single machine (6 molds) producing10-ounce cups or 16-ounce cups can range from about 30 to 100 cups perminute. Several machines can be used to increase the production rate.

It has been found that the coating composition also tends to improve therim strength of the container, which in effect, improves the overallstrength of the container. The rim strength is a measure of the forcerequired (in kilograms) to cause the rim to crumble a one-fourth inchdisplacement from the opened edge of the container.

The invention is further illustrated, but not limited by, the followingexamples.

EXAMPLES Examples 1-4

For Examples 1-4, expandable polystyrene beads (NOVA Chemical F271TU orF-271T) were first blended with component a) liquid polyethylene glycol400 (PEG 400) in a drum mixer. These PEG coated beads were then coatedwith the coating composition comprising the following components:polyethylene glycol 8000 (PEG 8000); and/or polyethylene wax (PE 1000T6); and/or zinc stearate (ZnS) in the amounts shown in Tables 1-4. Thedesignation PE 1000 T6 for the polyethylene wax indicates that thepolyethylene wax has an average molecular weight of about 1000 and aparticle size of about 6 microns. This polyethylene wax, PE 1000 T6 isavailable from the Baker Petrolite Corporation under the trademarkPETROLITE®.

Example 1

Five samples (I-V) were prepared by the following procedure:

3.8 pounds of impregnated NOVA Chemicals F271TU (expandable polystyrene)cup beads, ranging from 0.010 to 0.020 inch in diameter and containing5.6% by weight, based on the weight of the particles, of mixed pentane(n-pentane and isopentane in the ratio of 90:10), and for samples(II-V), liquid PEG 400 in the amounts shown in Table 1 were stir blendedin a drum container for 5 minutes. The components of the solid part ofthe coating composition in the amounts shown in Table 1 were added tothe mixture and the contents were further blended for another 5 minutes.

The impregnated, coated beads were pre-expanded in an 11-gallon RodmanSteam pre-expander (Artisan Industries Inc.) at atmospheric pressure.The pre-expansion was operated batch wise with a target pre-puff densityof 4.0 pounds per cubic foot (pcf). The newly prepared pre-puff was airdried for 5 minutes to remove the moisture and was allowed to age forabout 4 hours before molding.

Ten-ounce cups were molded using the aforesaid Autonational Cup MachineModel 6VLC-125 (standard molding conditions) and using the pre-expandedbeads with the densities indicated in Table 1. The steam header pressurewas 100 pounds per square inch (psi) and the total cycle time was about12 seconds. The molded cups were allowed to age overnight beforetesting.

Four cups for each sample (I-V) were tested by the following method: 1)Since the upper portion of the cup is the most vulnerable area forleakage, testing was done in this area. A circular piece of molded EPSmaterial was placed down into each cup so that the upper 20% to 30% ofthe cup was made available for testing. 2) 15 grams of oil-fried pastawere crushed and spread evenly on the circular piece of molded EPSmaterial so that the pasta occupied the upper 20 to 30% of the cup. 3) 3grams of red pepper powder were spread evenly onto the crushed pasta. 4)Each cup was tightly sealed with an adhesive label and plastic stretchfilm and placed in an oven at a temperature of 149° F. (65° C.) 5) Eachsample was checked for stains first every hour during a 7 hour periodand then once every 8 hours until failure for a maximum of 3 days.

The average time to failure (ATF) for each cup group sampling wascalculated by adding the time to failure for each container and dividingthe total time by the number of containers that were tested. The maximumATF value of 72 hours represents that none of the cups for the cup groupsampling exhibited any stain or leakage. The minimum ATF value of 1 hourrepresents that all of the cups in the cup group sampling failed withinthe first 1 hour.

Each cup in each cup group sampling (10 cups in each of these groupsamplings) was tested for rim strength (force applied on the cup rim at¼ inch displacement) and the average force was recorded.

The results for the stain resistance and rim strength are shown in Table1.

TABLE 1 I Sample (Control) II III IV V PEG 400 (g) - 5.17 3.50 3.50 0.90PE 1000 T6 (g) - 6.89 9.00 12.00 18.00 PEG 8000 (g) - - - - - ZnS (g)1.80 1.80 1.80 - - Density (pcf) 3.96 3.95 4.08 4.11 4.15 Rim Strength0.286 0.316 0.330 0.312 0.327 (kg) ATF (hour) 1.5 72 25 37.5 14

As Table 1 indicates, cups formed with impregnated polystyrene particlesthat were coated or covered with the coating composition of theinvention (Samples II-V) had improved rim strength and improved ATFcompared to the control cups (Sample I) that were formed with particlescoated only with zinc stearate.

Example 2

The procedure of Example 1 was repeated using the amounts and componentsshown in Table 2.

TABLE 2 I Sample (Control) VI VII VIII PEG 400 (g) - 0.60 3.50 3.45 PE1000 T6 (g) - - - - PEG 8000 (g) - - - 5.17 ZnS (g) 1.80 1.80 1.80 1.80Density (pcf) 3.96 3.95 4.05 3.84 Rim Strength 0.286 0.298 0.323 0.307(kg) ATF (hour) 1.5 1.0 3 27

As Table 2 indicates, cups (Samples VI-VIII) formed with impregnatedpolystyrene particles coated or covered with the coating composition ofthe invention had improved rim strength and in general improved ATFcompared to the control cups (Sample I) that were formed with particlescoated solely with zinc stearate.

Example 3

The procedure of Example 1 was repeated except that the expandablepolystyrene beads were substituted with beads containing 5.6% by weight,based on the weight of the beads, of normal pentane as the sole blowingagent.

TABLE 3 IX Sample (Control) X XI XII XIII PEG 400 (g) - 5.17 3.50 3.503.45 PE 1000 T6 (g) - 6.89 - 12.00 8.62 PEG 8000 (g) - - - - - ZnS (g)1.80 1.80 1.80 - 1.80 Density (pcf) 3.81 4.06 3.96 4.31 4.06 RimStrength 0.306 0.328 0.316 0.328 0.336 (kg) ATF (hour) 1.5 28 2 23 15

As Table 3 indicates, cups formed with polystyrene particles impregnatedwith 5.6% by weight, based on the weight of the particles, of normalpentane as the sole blowing agent and that were coated or covered withthe coating composition of the invention (Samples X through XIII) hadimproved rim strength and improved ATF compared to the control cups(Sample IX) that were coated solely with zinc stearate.

Example 4

The procedure of Example 3 was repeated except that the expandablepolystyrene beads were substituted with beads containing 5.65% byweight, based on the weight of beads, of normal pentane as the soleblowing agent and that were pre-lubricated with 0.0225% by weightsilicon oil. The beads were coated or covered with the components in theamounts shown in Table 4.

TABLE 4 Sample XIV (Control) XV PEG 400 (g) - 5.17 PE 1000 T6 (g) - 6.89PEG 8000 (g) - - ZnS (g) 1.80 1.80 Density (pcf) 3.98 4.13 Rim Strength(kg) 0.309 0.330 ATF (hour) 1.5 19

As Table 4 indicates, the cups formed with the expandable polystyreneparticles having 5.6% by weight, based on the weight of the beads, ofnormal pentane as the sole blowing agent and that were coated or coveredwith the coating composition of the invention (Sample XV) had improvedATF and improved rim strength compared to the control cups (Sample XIV)that were formed with beads coated only with zinc stearate.

Example 5

3.8 pounds of impregnated NOVA Chemicals F271TU (expandable polystyrene)cup beads, ranging from 0.010 to 0.020 inch in diameter and containing5.6% by weight, based on the weight of the beads, of normal pentane and1.80 grams of zinc stearate were stir blended in a drum container for 5minutes. The impregnated zinc stearate coated beads were pre-expanded inan 11-gallon Rodman Steam pre-expander (Artisan Industries Inc.) atatmospheric pressure. The pre-expansion was operated batch wise with atarget pre-puff density of 4.0 pounds per cubic foot (pcf). The newlyprepared pre-puff was air dried for 5 minutes to remove the moisture andwas allowed to age for about 4 hours. 0.65 pounds of the pre-puff beadswere stir blended with 2.95 grams polyethylene wax (PE 1000 T6) for 5minutes. The coated pre-puff beads were molded using Autonational CupMachine Model 6VLC-125 (standard molding conditions). The cup molding,the stain testing, and the rim strength testing were done similar tothat for Examples 1-4. The formulations and test results are shown inTable 5.

TABLE 5 Sample XVI (Control) XVII Bead Lubrication Bead Weight (lb.)3.80 3.80 Zinc Stearate (g) 1.80 1.80 Pre-Puff Lubrication - Pre-PuffWeight (lb) 0.65 0.65 PE 1000 T6 (g) - 2.95 Pre-Puff Density (pcf) 3.883.88 Rim Strength (kg) 0.301 0.301 ATF (hour) 1.5 39

Example 5 shows that cups (Sample XVII) formed with particles that werecoated or covered with the coating composition of the invention hadimproved ATF compared to the control cups (Sample XVI) formed withparticles covered or coated only with zinc stearate.

Example 6

Expandable polystyrene beads (NOVA Chemical F271TU) were first blendedwith liquid polyethylene glycol 400 (PEG 400) in a Ross ribbonmini-blender 42N-1/4S (Charles Ross & Son Company, Hauppauge, N.Y.).These PEG coated beads were then coated with a polyethylene wax in theamounts shown in Table 6 and selected from one of the following types ofwaxes: 1) PE 1000 T6, which is a polyethylene wax having an averagemolecular weight of about 1000 and a particle size of about 6 microns;2) PE 850 T10, which is a polyethylene wax having an average molecularweight of about 850 and a particle size of about 10 microns; 3) PE 655T10, which is a polyethylene wax having an average molecular weight ofabout 655 and a particle size of about 10 microns; and 4) PE 500 T60,which is a polyethylene wax having an average molecular weight of about500 and a particle size of about 60 microns. Zinc stearate (ZnS) wasused on all samples in the amounts shown in Table 6. The polyethylenewaxes are obtained from the Baker Petrolite Corporation under thetrademark PETROLITE®.

Five samples (XVIII-XXII) were prepared by the following procedure:

8 pounds of the impregnated, expandable polystyrene cup beads, rangingfrom 0.010 to 0.020 inch in diameter and containing 5.6% by weight,based on the weight of the particles, of normal pentane and liquid PEG400 in the amounts shown in Table 6 were blended in the mini-blender for10 minutes. The components of the solid part of the coating compositionin the amounts shown in Table 6 were added to this mixture and thecontents were further blended for another 10 minutes.

The impregnated, coated beads were pre-expanded in an 11-gallon RodmanSteam pre-expander (Artisan Industries Inc.) at atmospheric pressure.The pre-expansion was operated batch wise with a target pre-puff densityof 4.0-4.5 pounds per cubic foot (pcf). The newly prepared pre-puff wasair dried for 5 minutes to remove the moisture and was allowed to agefor about 4 hours before molding.

Sixteen-ounce cups were molded using a Master Cup Machine M10 (MasterMachine & Tool Co., Mulberry, Fla.) under standard molding conditions.The pre-expanded beads had the densities indicated in Table 6. The steamheader pressure was 100 pounds per square inch (psi) and the total cycletime was about 14.8 seconds. The molded cups were allowed to ageovernight before testing.

Four cups for each sample (XVIII-XXII) were tested by the followingmethod: 1) In a method similar to that set forth for Examples 1-4, oilfried pre-shaped Nissin cup noodles, available in the US market, wereplaced in each cup. 2) 3 grams of red pepper powder were spread evenlyonto the noodle surface. 3) Each cup was tightly sealed with an adhesivelabel and plastic stretch film, and placed in the oven at a temperatureof 149° F. (65° C.) 4) Each sample was checked for stains first everyhour during a 7 hour period and then once every 8 hours until failurefor a total of 72 hours or 3 days.

The average time to failure (ATF) was calculated similar to that setforth in Example 1. The maximum ATF value of 72 hours represents thatnone of the cups for the cup group sampling exhibited any stain orleakage. The minimum ATF value of 1 hour represents that all of the cupsin the cup group sampling failed within the first 1 hour.

The results for the stain resistance, in terms of ATF, are shown inTable 6.

TABLE 6 XVIII Sample (Control) XIX XX XXI XXII F271TU (lb) 8.0 8.0 8.08.0 8.0 PEG 400 (g) 10.9 10.9 10.9 10.9 10.9 PE 1000 T6 (g) - 14.5 - - -PE 850 T10 (g) - - 14.5 - - PE 655 T10 (g) - - - 14.5 - PE 500 T60(g) - - - - 14.5 ZnS (g) 3.8 3.8 3.8 3.8 3.8 Density (pcf) 4.07 4.394.36 4.50 4.36 ATF (hour) 1.8 41 23 28 30

As Table 6 indicates, cups formed with impregnated polystyrene particlesthat were coated or covered with the coating composition of theinvention (Samples XIX-XXII) had improved ATF compared to the controlcups (Sample XVIII) that were formed with particles coated only withzinc stearate.

Control Sample XVIII of Example 6 is compared to the samples of Examples7, 8, and 9.

Example 7

The procedure of Example 6 was repeated for Example 7. The beads werecoated or covered with the components in the amounts shown in Table 7.

TABLE 7 Sample XVIII (Control) XXIII F271TU (lb) 8.0 8.0 PEG 400 (g) -3.63 PEG 8000 (g) - 7.26 ZnS (g) 3.8 9.07 Density (pcf) 4.07 4.02 ATF(hour) 1.8 72

As Table 7 indicates, the cups formed with the expandable polystyreneparticles having 5.6% by weight, based on the weight of the beads, ofnormal pentane as the sole blowing agent and that were coated with thecoating composition of the invention (Sample XXIII) had improved ATFcompared to the control cups (Sample XVIII) that were formed with beadscoated only with zinc stearate.

Example 8

The procedure of Example 6 was repeated for Example 8 with thecomponents in the amounts shown in Table 8. The coated beads were agedfor 48 hours before pre-expansion.

TABLE 8 Sample XVIII (Control) XXIV F271TU (lb) 8.0 8.0 PEG 400 (g) -10.9 PE 1000 T60 (g) - 14.5 ZnS (g) 3.8 3.8 Density (pcf) 4.07 3.98 ATF(hour) 1.8 48

As Table 8 indicates, the cups formed with the expandable polystyreneparticles having 5.6% by weight, based on the weight of the beads, ofnormal pentane as the sole blowing agent that were coated or coveredwith the coating composition of the invention (Sample XXIV) had improvedATF compared to the control cups (Sample XVIII) that were formed withbeads coated solely with zinc stearate.

Example 9

The procedure of Example 7 was repeated. PEG 8000 was substituted withethylene bis-stearamide powder (available from the Crompton Corporationunder the trade mark KEMAMIDE® W-40). The beads were coated or coveredwith the components in the amounts shown in Table 9.

TABLE 9 XVIII Sample (Control) XXV F271TU (lb) 8.0 8.0 PEG 400 (g) -10.8 KEMAMIDE ® W-40 (g) - 14.5 ZnS (g) 3.8 3.8 Density (pcf) 4.07 4.18ATF (hour) 1.8 26

As Table 9 indicates, the cups formed with the expandable polystyreneparticles having 5.6% by weight, based on the weight of the beads, ofnormal pentane as the sole blowing agent, that were coated with thecoating composition of the invention (Sample XXV) had improved ATFcompared to the control cups (Sample XVIII) that were formed with beadscoated solely with zinc stearate.

Example 10

Expandable polystyrene beads (NOVA Chemical F271TU) were first blendedwith liquid polyethylene glycol 400 (PEG 400) in a drum mixer. These PEGcoated beads were then coated with polyethylene wax and zinc stearate(ZnS) in the amounts shown in Table 10. The polyethylene wax had anaverage molecular weight of about 1000 and a particle size of about 6microns. (PE 1000 T6 obtained from Baker Petrolite under the trademarkPetrolite®.)

Two samples (XXVI-XXVII) were prepared by the following procedure:

3.8 pounds of impregnated NOVA Chemicals F271TU (expandable polystyrene)cup beads, ranging from 0.010 to 0.020 inch in diameter and containing5.6% by weight, based on the weight of the particles, of normal pentane.

For sample XXVII, liquid PEG 400 in the amount shown in Table 10 wasstir blended with the particles in a drum container for 5 minutes. Thepolyethylene wax (PE 1000 T6) and zinc stearate in the amounts shown inTable 10 were added to this mixture and the contents were furtherblended for another 5 minutes.

The impregnated, coated beads were pre-expanded in an 11-gallon RodmanSteam pre-expander (Artisan Industries Inc.) at atmospheric pressure.The pre-expansion was operated batch wise with a target pre-puff densityof 4.0 pounds per cubic foot (pcf). The newly prepared pre-puff was airdried for 5 minutes to remove the moisture and was allowed to age forabout 4 hours before molding.

Ten-ounce cups were molded using Autonational Cup Machine Model 6VLC-125(standard molding conditions) and using the pre-expanded beads havingthe densities indicated in Table 10. The steam header pressure was 100pounds per square inch (psi) and the total cycle time was about 12seconds. The molded cups were allowed to age overnight before testing.

Ten cups for each sample (XXVI-XXVII) were tested by the followingmethod: Coffee at 170° F. was poured into each cup and the side wallsand bottom of each cup containing coffee were observed for coffee stainsor leakage every 15 minutes for the first 2 hours, every one hour from 2to 6 hours, and then every 8 hours until failure or for a maximum of 6days.

The average time to failure (ATF) was calculated similar to that setforth in Example 1. The maximum ATF value of 144 hours represents thatnone of the cups for the cup group sampling exhibited any stain orleakage. The minimum ATF value of 0.25 hour represents that all of thecups in the cup group sampling failed within the first 15 minutes.

The results for coffee resistance are shown in Table 10.

TABLE 10 Sample XXVI (Control) XXVII F271TU (lb) 3.8 3.8 PEG 400 (g) -5.17 PE 1000 T6 (g) - 6.89 ZnS (g) - 1.81 Density (pcf) 3.88 3.96 ATF(hour) 2.9 144

As Table 10 indicates, cups formed with impregnated polystyreneparticles that were coated or covered with the coating composition ofthe invention (Sample XXVII) had improved ATF compared to the controlcups (Sample XXVI) that were formed with particles coated solely withzinc stearate.

The impregnated thermoplastic particles coated or covered with thecoating composition of the invention can be used to form foam containersthat hold pre-packaged foods, e.g. instant noodles and/or soups, stews,meats, etc. that are sold on the shelves in the grocery store.

While the present invention has been set forth in terms of specificembodiments thereof, it will be understood in view of the instantdisclosure that numerous variations upon the invention are now enabledyet reside within the scope of the invention. For example, even thoughfoam containers are specifically described herein, it is to beunderstood, that the coating composition for thermoplastic resinparticles may be used to form other types of molded articles.Accordingly, the invention is to be broadly construed and limited onlyby the scope and spirit of the claims now appended hereto.

1. A method for improving the resistance to leakage of a foam containercomprising: obtaining expandable polystyrene particles having a diameterfrom about 0.008 to about 0.03 inches; impregnating the expandablepolystyrene particles with a blowing agent; applying a coatingcomprising liquid polyethylene glycol to the expandable polystyreneparticles; applying a solid component comprising a metal salt of higherfatty acids selected from the group consisting of zinc, magnesium,calcium, and aluminum salt of stearic, lauric, and myristic acid to thepolystyrene particles; pre-expanding the expandable polystyreneparticles to a density of from about 2 to about 12 pounds per cubic footto form pre-expanded particles; and heating the pre-expanded particlesin a closed mold to further expand and form a foam container.
 2. Themethod according to claim 1, wherein the liquid polyethylene glycol hasan average molecular weight ranging from about 200 to about
 800. 3. Themethod according to claim 1, wherein the amount of liquid polyethyleneglycol on the polystyrene particles is from about 0.01% to about 0.80%by weight based on the weight of the particles.
 4. The method accordingto claim 1, wherein the amount of the metal salt of higher fatty acid onthe polystyrene particles is from about 0.01% to about 0.60% by weight,based on the weight of the particles.
 5. The method according to claim 1wherein the amount of liquid polyethylene glycol on the polystyreneparticles is about 0.30% and the amount of the metal salt of higherfatty acid is about 0.105% by weight, based on the weight of theparticles.
 6. The method according to claim 1 wherein the metal salt ofhigher fatty acid is zinc stearate.
 7. A method for improving theresistance to leakage of a foam container comprising: obtainingexpandable polystyrene particles having a diameter from about 0.008 toabout 0.03 inches; impregnating the expandable polystyrene particleswith a blowing agent; applying a coating comprising liquid polyethyleneglycol having an average molecular weight ranging from about 200 toabout 800 to the expandable polystyrene particles in an amount of fromabout 0.01% to about 0.80% by weight based on the weight of theparticles; applying a solid component comprising a metal salt of higherfatty acids selected from the group consisting of zinc, magnesium,calcium, and aluminum salt of stearic, lauric, and myristic acid to thepolystyrene particles in an amount of from about 0.01% to about 0.60% byweight, based on the weight of the particles; pre-expanding theexpandable polystyrene particles to a density of from about 2 to about12 pounds per cubic foot to form pre-expanded particles; and heating thepre-expanded particles in a closed mold to further expand and form afoam container.
 8. The method according to claim 7 wherein the amount ofliquid polyethylene glycol on the polystyrene particles is about 0.30%and the amount of the metal salt of higher fatty acid is about 0.105% byweight, based on the weight of the particles.
 9. The method according toclaim 7 wherein the metal salt of higher fatty acid is zinc stearate.